diff --git a/components/metrics/lib.rs b/components/metrics/lib.rs
index 7e7cd9afd1d..bd2d488f100 100644
--- a/components/metrics/lib.rs
+++ b/components/metrics/lib.rs
@@ -40,6 +40,7 @@ pub trait ProgressiveWebMetric {
     fn send_queued_constellation_msg(&self, name: ProgressiveWebMetricType, time: u64);
 }
 
+/// TODO make this configurable
 /// maximum task time is 50ms (in ns)
 pub const MAX_TASK_NS: u64 = 50000000;
 /// 10 second window (in ns)
@@ -84,6 +85,7 @@ fn set_metric<U: ProgressiveWebMetric>(
 
     // Print the metric to console if the print-pwm option was given.
     if opts::get().print_pwm {
+        println!("Navigation start: {}", pwm.get_navigation_start().unwrap());
         println!("{:?} {:?}", metric_type, time);
     }
 
@@ -216,6 +218,10 @@ impl InteractiveMetrics {
     pub fn get_tti(&self) -> Option<u64> {
         self.time_to_interactive.get()
     }
+
+    pub fn needs_tti(&self) -> bool {
+        self.get_tti().is_none()
+    }
 }
 
 impl ProgressiveWebMetric for InteractiveMetrics {
diff --git a/components/script/dom/document.rs b/components/script/dom/document.rs
index 5214ea4da66..c9130ad5e44 100644
--- a/components/script/dom/document.rs
+++ b/components/script/dom/document.rs
@@ -97,7 +97,7 @@ use hyper_serde::Serde;
 use ipc_channel::ipc::{self, IpcSender};
 use js::jsapi::{JSContext, JSRuntime};
 use js::jsapi::JS_GetRuntime;
-use metrics::{InteractiveFlag, InteractiveMetrics, InteractiveWindow, ProfilerMetadataFactory};
+use metrics::{InteractiveFlag, InteractiveMetrics, InteractiveWindow, ProfilerMetadataFactory, ProgressiveWebMetric};
 use msg::constellation_msg::{BrowsingContextId, Key, KeyModifiers, KeyState, TopLevelBrowsingContextId};
 use net_traits::{FetchResponseMsg, IpcSend, ReferrerPolicy};
 use net_traits::CookieSource::NonHTTP;
@@ -1911,6 +1911,10 @@ impl Document {
         self.dom_interactive.get()
     }
 
+    pub fn set_navigation_start(&self, navigation_start: u64) {
+        self.interactive_time.borrow_mut().set_navigation_start(navigation_start);
+    }
+
     pub fn get_interactive_metrics(&self) -> Ref<InteractiveMetrics> {
         self.interactive_time.borrow()
     }
@@ -1940,7 +1944,9 @@ impl Document {
     }
 
     pub fn start_tti(&self) {
-        self.tti_window.borrow_mut().start_window();
+        if self.get_interactive_metrics().needs_tti() {
+            self.tti_window.borrow_mut().start_window();
+        }
     }
 
     /// check tti for this document
@@ -1948,7 +1954,6 @@ impl Document {
     /// main thread available and try to set tti
     pub fn record_tti_if_necessary(&self) {
         if self.has_recorded_tti_metric() { return; }
-
         if self.tti_window.borrow().needs_check() {
             self.get_interactive_metrics().maybe_set_tti(self,
                 InteractiveFlag::TimeToInteractive(self.tti_window.borrow().get_start()));
diff --git a/components/script/script_thread.rs b/components/script/script_thread.rs
index 5cd9261ed2b..d969a46fecc 100644
--- a/components/script/script_thread.rs
+++ b/components/script/script_thread.rs
@@ -1248,6 +1248,9 @@ impl ScriptThread {
         for (doc_id, doc) in self.documents.borrow().iter() {
            if let Some(pipeline_id) = pipeline_id {
                 if pipeline_id == doc_id && end - start > MAX_TASK_NS {
+                    if opts::get().print_pwm {
+                        println!("Task took longer than max allowed ({:?}) {:?}", category, end - start);
+                    }
                     doc.start_tti();
                 }
             }
@@ -2229,6 +2232,7 @@ impl ScriptThread {
         let parse_input = DOMString::new();
 
         document.set_https_state(metadata.https_state);
+        document.set_navigation_start(incomplete.navigation_start_precise);
 
         if is_html_document == IsHTMLDocument::NonHTMLDocument {
             ServoParser::parse_xml_document(&document, parse_input, final_url);